When drilling oil and gas wells with rotary drilling equipment, the drill pipe frequently comes into contact with the well casing, resulting in wear to both the casing and the drill pipe. In addition, the friction between the drill pipe and casing may result in significant torque and drag, which can exceed the capability of the rig's drive system. Drill pipe protectors are commonly known in the industry. They generally comprise a protective sleeve made from a non-abrasive material secured to the drill pipe. The sleeve is positioned on the drill pipe so that the sleeve can contact the wall of the well casing or bore to prevent damaging contact between the rotating drill pipe and the casing or bore.
The prior art includes use of various types of rotating and non-rotating drill pipe protectors. The most prevalent rotating protector design uses a wedge-shaped stamped steel “wedge pin” which is driven into the hinge to close the protector around the drill pipe. Non-rotating drill pipe protectors (NRDDPs) are disclosed in several U.S. patents held by Western Well Tool, Inc. (WWT), including U.S. Pat. No. 5,069,297 to Krueger et al. These patents disclose techniques for producing a fluid bearing effect between the sleeve and the drill pipe so that the drill pipe can rotate relative to the protective sleeve during use.
The present invention is directed to rotating drill pipe protectors (RDPPs). These protectors are rigidly affixed to the drill pipe so they can rotate with the drill pipe during use. Generally speaking, these drill pipe protectors can be of lower cost than NRDPPs, particularly for use on land-based rigs. They can be effective in offering protection in applications involving moderate side loads. RDPPs must be designed to generate a substantial circumferential gripping strength that minimizes axial slippage between the sleeve and the drill pipe in response to side loads caused by contact forces between the sleeve and the well casing or bore during use. Low grip strength around the pipe can frequently result in the protector slipping on the pipe; and when the protectors move away from their installed position, they become ineffective at preventing wear. Also, problems are caused by the inability to strip through pressure control equipment, such as diverter assemblies, rotating pressure control heads, and BOPs, due to low grip strength. Once the protector has slipped, its structural integrity is too often inadequate to prevent serious failure of the protector, resulting in debris in the well.
The previously mentioned stamped steel wedge pin design produces low holding forces and leaves a significant portion of the pin remaining above the protector where it can hang-up on obstructions.
A frequent problem offshore is in drilling with a riser in deep water. Drill pipe in these conditions may wear the riser, well head, and BOP equipment at significant cost and rig downtime. Use of rotating protectors, properly positioned, can prevent such damage and economic loss. However, this is an extremely demanding application, requiring large holding forces for RDPPs.
The present invention provides a rotating drill pipe protector that resists slippage by a protector sleeve attachment and fastener assembly having improved gripping strength. Other improvements also are provided. One area of improvement has to do with preventing buckling of the drill string during use.
Buckling of drill pipe has been and remains a serious problem to drilling by reducing the drilling penetration, damaging drill pipe, and sometimes preventing reaching the reservoir. The typical indication of buckling is the buckled pipe preventing placing load onto the drill bit, thus preventing drilling. Buckling of drill pipe is typically described by the buckling load, i.e., the load when the pipe buckles.
The buckling load is affected by many parameters including length of the drill pipe between tool joints, drill pipe diameter, tool joint diameter, diameter of casing or open hole, the eccentricity of the drill pipe within the casing, the fluid (weight and lubricity), coefficient of friction between the drill pipe and casing in the fluid, stiffness of the drill pipe (Young's Modulus), hole curvature (dog leg severity), rotational speed of the drill pipe in the casing, rate of advancement downhole (sliding or rotating), the moment of inertia of the drill pipe, the wall thickness of the drill pipe, the boundary conditions describing how the bit is reacting to the formation at the bottom of the well, as well as other parameters. Several commercially available software packages predict buckling load for drill strings.
Some analytical models of buckling identify the importance of the unsupported length of the drill pipe as having a strong influence on the buckling load. Methods have been used to effectively reduce the unsupported length of drill pipe or otherwise for increasing the buckling load. Specifically, for some applications thicker wall thickness pipe is used, and in other designs stabilizer blades are placed in the drill string between drill pipe points. In other design used by Western Well Tool, a non-rotating drill pipe protector is placed in the center of the drill pipe.
The use of non-rotating drill pipe protectors to prevent buckling has been successful in increasing the buckling load, but at a cost. First, non-rotating drill pipe protectors are expensive and can be subject to damage because of the extremely high side loads at or near buckling.
Rotating protectors are typically not used to prevent buckling. Typically, rotating protectors are placed within 10 feet of the tool joints in both the 31 foot length (Range 2 drill pipe) and 45 foot length (Range 3) drill pipe. The reason is that existing rotating drill pipe protectors have poor gripping capability and cannot withstand the loads seen at or near buckling.
The present invention addresses the problems of providing a means to effectively reduce the unsupported length, resisting the resulting side loads on the drill pipe from large compressive loads, and performing these tasks economically, using the rotating drill pipe protector of this invention.